Tag: Temperature- controlled weathering

A University of Chicago- led study (published in Nature Communications in 2026) suggests Earth’s long- term climate “thermostat”, driven by silicate weathering that regulates atmospheric CO₂, operated primarily in a temperature- dominated mode for most of the past ~480 million years, but briefly switched to a hydrology (water and rainfall)- dominated mode during the Pangea supercontinent era (~295- 200 million years ago), then switched back.

Earth has stayed habitable for billions of years partly because of negative feedback in the carbon cycle. Atmospheric CO₂ reacts with rainwater to form a weak acid that weathers silicate rocks; the dissolved minerals and carbon wash into oceans and eventually form carbonate rocks.

Over geologic time these are subducted, and volcanoes return CO₂ to the atmosphere. Faster weathering cools the planet (by drawing down CO₂); slower weathering allows CO₂ to build up and warm it.

Scientists have long debated whether temperature (chemical reactions speed up when warmer) or hydrology (the amount of water available to dissolve and transport minerals) is the main control on weathering rates. The water-limited (hydrologic) mode is considered a weaker, less efficient thermostat that could permit larger climate swings while still balancing carbon fluxes.

R.J. Graham (first author, UChicago postdoc), with colleagues including Dorian Abbot and B.B. Cael (UChicago) and collaborators from the University of Southampton, ran ~120 climate- model simulations that were identical except for randomly generated continent layouts. They calculated weathering under both temperature- driven and hydrology- driven assumptions and looked for geographic “fingerprints”:

• Temperature- controlled weathering correlates with the amount of land in the tropics (hotter but not necessarily wetter, because extra rain can evaporate).
• Hydrology- controlled weathering correlates with how fragmented or consolidated the continents are (more coastlines and runoff favor greater water availability).⁠

Because stronger weathering cools the climate, each mode predicts an anti-correlation between global temperature and its controlling geographic variable.

The team then compared a 480- million- year temperature reconstruction with paleogeographic maps of ancient continents.

For most of the interval, temperatures anti- correlated with tropical land fraction, consistent with temperature- dominated weathering.

For roughly 100 million years overlapping the existence of Pangea, the pattern flipped to anti- correlation with continental fragmentation (i.e., the hydrology signature). The researchers attribute this to Pangea’s extensive arid interior, which limited water flow through soils so that water availability, rather than temperature, became the primary limit on weathering.

The modeling used idealized conditions (no mountain ranges, varying rock types, vegetation, etc.), relied on particular paleogeographic reconstructions, and assumed relatively steady volcanic CO₂ output. Ancient soil records from the Pangea interval could help test the idea further.⁠

If the thermostat can switch modes, it has broader relevance: a less efficient (hydrology- limited) feedback could affect the width of the “Goldilocks” (habitable) zone around stars, because the CO₂- weathering feedback is a key assumption in defining the range of orbits where liquid water, and potentially life, can persist.⁠

The paper is “Paleogeographic controls on Phanerozoic weathering rates and implications for climate regulation” (Graham, Cael, Fu, Abbot et al., Nature Communications, 2026; DOI: 10.1038/s41467-026-77289-3), with NASA funding. The University of Chicago News piece summarizing it was written by Maureen Searcy.

Pangea’s vast arid interior limited water availability, which made silicate weathering primarily hydrology- controlled (limited by water supply) rather than temperature- controlled.

In the UChicago- led study, this aridity is the proposed reason the climate “thermostat” briefly switched modes for roughly 100 million years while the supercontinent existed.

With much of the landmass far from ocean moisture sources, large interior regions experienced low rainfall and reduced water flow through soils. As a result, water (or the lack of it) became the main limiting factor on the chemical breakdown of silicate rocks that draws down atmospheric CO₂, rather than reaction rates speeding up with heat.

This hydrologic limitation produces a weaker, less efficient negative feedback than temperature- driven weathering. It is consistent with the geologic temperature record showing an anti- correlation with continental fragmentation (rather than tropical land area) during the Pangea interval.

Broader paleoclimate context supports the idea of an arid interior: the supercontinent’s size created strong continental climates with extensive deserts, extreme seasonal contrasts, and limited moisture penetration inland, even while coastal and equatorial margins could be wetter.

Paleogeographic controls on Phanerozoic weathering rates and implications for climate regulation

Earth’s long- term climate stability is widely attributed to negative feedback from silicate weathering, which consumes atmospheric CO₂ faster as the climate warms.

A key uncertainty remains: is this feedback driven primarily by temperature (kinetic control on mineral dissolution rates) or by hydrology (runoff and water flux through the weathering zone)?

The authors ran a large ensemble of idealized global climate model (GCM) simulations that were identical except for randomized continental configurations. They then calculated global silicate weathering rates under two end-member assumptions:

• Temperature- controlled weathering (exponential dependence on temperature, no direct runoff dependence)
• Hydrology- controlled weathering (linear dependence on runoff, no direct temperature dependence)

They identified distinct geographic “fingerprints”:

• Temperature- controlled weathering correlates strongly with tropical land fraction (TLF; land between 15°N/S).
• Hydrology- controlled weathering correlates strongly with continental fragmentation (continental perimeter divided by area).

Because stronger weathering draws down CO₂ and cools the planet, each regime predicts an anti- correlation between global mean surface temperature (GMST) and its controlling geographic variable.

They compared a 480- million- year GMST reconstruction with paleogeographic reconstructions:

• For most of the past 480 million years, GMST is anti- correlated with tropical land fraction → consistent with temperature- dominated control.
• From roughly 295 to 200 million years ago (overlapping the existence of the supercontinent Pangea), the relationship flips: GMST becomes anti- correlated with continental fragmentation → consistent with hydrology-dominated control.
• After ~200 Ma the temperature- controlled signature returns.

The authors suggest Pangea’s extensive arid interior reduced water availability across large areas of land, so that runoff (or the lack of it) became the primary limit on weathering rates rather than temperature.

Implications and caveats

• The hydrology- limited regime is a weaker thermostat, potentially allowing larger climate swings.
• The result relies on assumptions including relatively steady volcanic outgassing, a tight CO₂- temperature link, and the accuracy of paleogeographic reconstructions.
• The GCM experiments are idealized (flat topography, no mountains, uniform lithology, no vegetation effects, no seafloor weathering, etc.).

The study provides evidence that the dominant control on Earth’s silicate-weathering thermostat may have shifted during the Phanerozoic, with temperature control dominant for most of the interval examined but hydrology control temporarily dominant during the Pangea era.

Journal: Nature Communications

DOI: 10.1038/s41467-026-77289-3

Provided: University of Chicago

Authors: R. J. Graham,
B. B. Cael,
M. Fu &
D. S. Abbot

Abstract

Earth’s climate has remained habitable for billions of years, a stability usually attributed to a negative feedback from silicate weathering – the chemical breakdown of silicate rocks on land, which consumes atmospheric carbon dioxide faster as climate warms. However, whether temperature or hydrology primarily drives this feedback remains uncertain. Here we show the two controls leave geographic fingerprints: in an ensemble of climate simulations with randomized continents, temperature-controlled weathering depends on tropical land fraction, whereas hydrology-controlled weathering depends on continental fragmentation. Stronger weathering removes more carbon dioxide, cooling the planet, so each regime predicts anti-correlation between temperature and its controlling geography. Reconstructed global temperatures spanning 480 million years are anti-correlated with tropical land fraction, except from roughly 295 to 200 million years ago – overlapping the supercontinent Pangea – when they anti-correlate with continental fragmentation. The mechanism stabilizing Earth’s climate may thus have evolved, with temperature control apparently dominant for most of this period.